Apoptosis can be induced by a variety of extracellular and intracellular stimuli, one of which is radiation. This chapter focuses on the possible role of membrane events in inducing apoptosis, particularly in relation to the radiation response of lymphoid cells. Classically, radiation-induced cell death has been defined as either interphase or reproductive death. Apoptosis can be induced with stimuli that trigger specific receptors in the plasma membrane that activate signal transduction. The protooncogene bcl-2 has been implicated as a component of the molecular process that determines whether a cell lives or undergoes apoptosis. Several membrane-associated kinases and phosphatases which appear to play a role in apoptosis are altered after radiation exposure. Another very important second messenger involved in the apoptotic death program is calcium. Agents and reactions that modify chromatin structure or nuclease activity can either prevent or induce DNA fragmentation. Radiation exposure results in the production of reactive oxygen intermediates and the induction of membrane lipid peroxidation chain reactions.

The use of depleted uranium in armor-penetrating munitions remains a source of controversy because of the numerous unanswered questions about its long-term health effects. Although no conclusive epidemiologic data have correlated DU exposure to specific health effects, studies using cultured cells and laboratory rodents continue to suggest the possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure. Until issues of concern are resolved with further research, the use of depleted uranium by the military will continue to be controversial.

This chapter aims to summarize the status of knowledge about the potential health effects of Depleted uranium (DU) based on cellular and animal studies. Studies have been conducted using cultured cells and animal models and have attempted to answer questions relating to toxicity, carcinogenicity, and involvement of radioactivity. Uranium was discovered in the mineral pitchblende in 1789 by the German chemist Martin Heinrich Klaproth. Uranium does not exist in pure metallic form in nature because it is quickly oxidized in air. Toxicology studies of natural uranium partially relevant to understanding DU health effects are numerous, beginning with the first reported observations of uranium-induced kidney abnormalities in the mid-1800s. The neurophysiological effects of uranium exposure have been investigated for many decades. Among the early findings was the observation that uranyl ions potentiate the twitch response of frog sartorious muscles by prolonging the active state of contraction.

This paper discusses the development of and proposed enhancements to a colorimetric test for the detection of uranium in biological samples such as urine. The goal of this work is to develop a technique for the detection of uranium that could: 1) be conducted rapidly and accurately; 2) would not require extensive sample preparation; 3) would not require expensive or complicated instrumentation; 4) would require little or no technical training to conduct; and 5) could be used in a field situation if needed. The technique described in this paper involves the following steps. A buffer is added to the sample to maintain the pH of the mixture within an experimentally acceptable range and a quaternary ammonium salt is added to aid in solubilization of the reaction components. A pyridylazo stain, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, capable of binding a variety of metals, is used to complex the uranium. This interaction has been made specific for uranium through the use of “masking agents.” Color development indicating the presence of uranium is monitored and can be quantitated by determining the absorbance of the reaction mixture at 578 nm, using a spectrophotometer or colorimeter. At present, the limit of sensitivity of the procedure is approximately 30 µg of uranium/L. However, through the incorporation of a sample concentration step in the procedure, we believe we can greatly increase the sensitivity of the technique. The two areas we believe are amenable to our concentration efforts are prior to the addition of the assay components (pre-complexation concentration step) or after the formation of the stain/uranium complex (post-complexation concentration step). Our goal is to make the procedure more applicable while still maintaining technical simplicity and ease of use. We believe this research will provide the capability to rapidly and accurately screen biological samples for uranium.

It is known that radiation can induce a transmissible persistent destabilization of the genome. We have established an in vitro cellular model using HOS cells to investigate whether genomic instability plays a role in depleted uranium (DU)-induced effects. Transmissible genomic instability, manifested in the progeny of cells exposed to ionizing radiation, has been characterized by de novo chromosomal aberrations, gene mutations, and an enhanced death rate. Cell lethality and micronuclei formation were measured at various times after exposure to DU, Ni, or gamma radiation. Following a prompt, concentration-dependent acute response for both endpoints, there was de novo genomic instability in progeny cells. Delayed reproductive death was observed for many generations (36 days, 30 population doublings) following exposure to DU, Ni, or gamma radiation. While DU stimulated delayed production of micronuclei up to 36 days after exposure, levels in cells exposed to gamma-radiation or Ni returned to normal after 12 days. There was also a persistent increase in micronuclei in all clones isolated from cells that had been exposed to nontoxic concentrations of DU. While clones isolated from gamma-irradiated cells (at doses equitoxic to metal exposure) generally demonstrated an increase in micronuclei, most clonal progeny of Ni-exposed cells did not. These studies demonstrate that DU exposure in vitro results in genomic instability manifested as delayed reproductive death and micronuclei formation.

The first large-scale combat use of depleted uranium (DU) weapons occurred during the Gulf War, and some U.S. personnel were wounded by DU fragments. Established fragment removal policies dictated that embedded metal fragments be left in place unless doing so posed unacceptable additional risks. However, questions were raised as to whether these policies are appropriate for a metal that--unlike lead, steel, or others--is chemically toxic and emits low-level radiation. Data from research currently under way indicate that long-term exposure to embedded DU fragments may present a level of risk that requires modification of established policies. Our understanding of DU health effects and of the possible mechanisms by which DU might affect tissues is evolving. Understanding more about the long-term response of tissues exposed to DU could facilitate future development of treatments for DU injuries.

Depleted uranium is a dense heavy metal used primarily in military applications. Published data from our laboratory have demonstrated that exposure to depleted uranium in vitro can transform immortalized human osteoblast (HOS) cells to the tumorigenic phenotype (associated with aberrant RAS oncogene expression and tumor suppressor protein production). Since depleted uranium is used in military applications, it would therefore be beneficial to identify and test potential antitumor-promoting agents. Chemopreventive interventions that target deregulated signal transduction pathways may be effective strategies to prevent carcinogenesis. Since the RAS protein plays a key role in signal transduction, disruption of its signaling pathway may be particularly effective. The phenyl fatty acid, phenyl acetate, a differentiation inducer that affects post-translational processing of RAS, was tested for its ability to prevent depleted uranium-induced neoplastic transformation using HOS cells. After a 24-h exposure to insoluble depleted uranium-uranium dioxide (1 mg/ml), cells were incubated for 1 day to 6 weeks with 2.5 mM phenyl acetate. Treatment with depleted uranium resulted in transformation to the tumorigenic phenotype. In contrast, HOS cells exposed to depleted uranium and then treated with phenyl acetate did not exhibit transformation to the tumorigenic phenotype, These data suggest that depleted uranium-induced neoplastic transformation in vitro can be prevented by targeting the RAS protein. (C) 2001 by Radiation Research Society.

The health effects of embedded fragments of depleted uranium (DU) are being investigated to determine whether current surgical fragment-removal policies are appropriate for this metal. The authors studied rodents implanted with DU pellets as well as cultured human cells exposed to DU compounds. Results indicate that uranium from implanted DU fragments distributes to tissues distant from implantation sites, including bone, kidney, muscle, and liver. Despite levels of uranium in kidney that would be nephrotoxic after acute exposure, no histological or functional kidney toxicity was observed with embedded DU, indicating that the kidney adapts when exposed chronically. Nonetheless, further studies of the long-term health impact are needed. DU is mutagenic and transforms human osteoblastic cells into a tumorigenic phenotype. It alters neurophysiological parameters in rat hippocampus, crosses the placental barrier, and enters fetal tissue. Preliminary data also indicate decreased rodent litter size when animals are bred 6 months or longer after DU implantation.

This laboratory previously reported that thermotolerance diminishes the NaCN-induced increase in intracellular free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells and that blocking this increase protects the cells from NaCN toxicity. In this study, we report that cell viability after exposure to NaCN (10 mM, 1 h) is enhanced by the overexpression of HSP-70 resulting from heat shock (45 degrees C, 10 min), treatment with a protein kinase C activator phorbol 12 myristate 13-acetate (PMA; 1 microM, 4 h), or HSP-70 cDNA transfection. Because the toxicity of NaCN is mediated by increases in [Ca2+]i, we sought to determine whether the overexpression of HSP-70 might protect the cells by altering the [Ca2+]i response induced by NaCN. Basal [Ca2+]i in vector-, HSF1 cDNA-, and HSP-70 cDNA-transfected cells was 114 +/- 11 (n = 11), 95 +/- 5 (n = 6), and 151 +/- 11 (n = 15) nM, respectively, suggesting that HSP-70 metabolism is associated with maintenance of resting [Ca2+]i. Removal of external Ca2+ reduced the resting [Ca2+]i in all of these cells. With external Ca2+ reduced the resting [Ca2+]i by 97 +/- 21% in vector-transfected cells and 111 +/- 5% in HSF1 vector-transfected cells but by only 27 +/- 8% in HSP-70 cDNA-transfected cells. Heat shock or PMA treatment of vector- or HSF1 cDNA-transfected cells to induce HSP-70 also attenuated the NaCN-induced increase in [Ca2+]i, perhaps because of a decrease in Vmax for the uptake of external Ca2+. Removal of external Ca2+ or treatment with inhibitors of Na+/Ca2+ exchangers eliminated the NaCN-induced increase in [Ca2+]i in HSP-70 cDNA-transfected cells, but ryanodine treatment did not. HSP-70 cDNA transfection also reduced Ca2+ mobilization stimulated by various Ca(2+)-mobilizing agents. The results suggest that HSP-70 overexpression protects cells from NaCN cytotoxicity, perhaps by attenuating the [Ca2+]i response.

This paper examines the factors influencing theyield — the proportion of accepted applicants that confirm their intention to attend — in the admissions process for the MBA program of the school of management at a large metropolitan university. A stochastic model of a student's MBA program choice decision is presented. Using the resulting logistic probability model, the authors examine the impact of student traits (both aptitude-related and non-aptitude-related) and program characteristics, known to admissions officials, on the probability of confirmation. The results of the analysis provide a basis for measuring the dimensions of the market for educational services this MBA program provides, suggest a strategic response to this market, and offer a way to measure the profitability of various strategic response options. In particular, the results demonstrate that financial aid awards can increase dramatically the probability of confirmation and that confirmation probabilities are affected significantly by non-aptitude-related student characteristics.

To investigate the role of the Ca2+-binding protein calmodulin on histamine release in the rat peritoneal mast cell, we exposed cells to exogenous calmodulin in the presence of a variety of histamine secretagogues. Histamine release stimulated by compound 48/80, polymyxin B and ionophore A23187 was inhibited while concanavalin A-stimulated release was not affected. Calmodulin in the presence of the secretagogues did not affect cell viability and calmodulin alone had no effect on histamine release. No direct interaction between calmodulin and the secretagogues was observed. Exogenous calmodulin does not appear to be incorporated into the cell. The inhibition of histamine release by calmodulin can be explained as a labile interaction between the protein and the cell that requires externally-bound Ca2+. These experiments demonstrate the use of exogenous calmodulin as a probe in the study of the mechanism of histamine release.

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